Diels-Alder Reactions of Vinyl Derivatives of Five-Membered Monoheterocyclic Compounds

Vinylpyrroles having electron-withdrawing substituents react with dienophiles to give [4 + 2] π adducts while the furan and thiophene analogues do not The difference in reactivity among the monoheterocycles can be explained in terms of the greater electron-releasing ability of the nitrogen atom in the pyrrole. The s-cis conformation of the (lif-pyrroi-2-yl)maleate derivatives appears to be an important factor in their undergoing the cycloaddition reaction.